Smell from drain

[drpepe]

I know nothing about drains so please bear with me as our drains have started stinking the garden up & the house when the doors/windows are open (internally no smell).

We have a linear drain that runs around our utility and extension into a combined waste/rain water drain - red arrows in pic show where it goes under the utility & the route is shown on the attached floor plan. The red rectangle in the utility represents a sealed drain cover. The extension was a conservatory til just a few weeks ago & is built on the same footprint - builders are finishing it off currently, but haven't touched the drainage at all.

The smell is coming from the corner where the linear drains go under the utility.

We moved into the house early '21 so I only have last summer to go on, but there was no smell then.

1. Is this setup of drains being 'open' in that corner ok?
2. Why would it start smelling now? I thought it was a summer heat thing but 1. we had no issues last year & 2. I have been sluicing it (also with bleach) but the smell continues
3. Could a culprit be debris from the builders going down there, but there's no evidence of the drain being blocked.
4. Also since the building work started we have been without a kitchen so are using the sink in the utility (see floorplan) to do our washing up. The sink drains into the linear drain - so a small amount of food might enter the drain, but also a lot sluicing from regular use.
5. What's the best way to investigate this?

Many thanks, comments appreciated!

 

[^woody^]

All waste drainage is either physically sealed or sealed with a water trap to stop smells getting out at low level.

If you have a drain smell, you have a drain problem.

 

[Hugh Jaleak]

Channel drainage should be for rainwater only, and if going to a combined sewer, needs to connected using a Trap or via a Trapped Gully. Drains will hum a bit more during warmer weather, the characteristics of sewage change so the odour changes with it.

Check channel drain outlet has a trap on it, if it doesn't (and is connected to the foul/combined drainage system), it needs a trap retrofitting. No amount of washing down or bleach is going to negate the need for a trap.

 

[drpepe]

Channel drainage should be for rainwater only, and if going to a combined sewer, needs to connected using a Trap or via a Trapped Gully. Drains will hum a bit more during warmer weather, the characteristics of sewage change so the odour changes with it.

Check channel drain outlet has a trap on it, if it doesn't (and is connected to the foul/combined drainage system), it needs a trap retrofitting. No amount of washing down or bleach is going to negate the need for a trap.

I am presuming there's a gully under the sealed cover in the utility room (which I need to open to check for issues)

Are you saying there should also be a trap at the inlet where the linear drain goes under the building?

 

[Hugh Jaleak]

Are you saying there should also be a trap at the inlet where the linear drain goes under the building?

If connected to a Combined Drainage system then Yes, it is a requirement under Building Regulations. Trap is your first line of defence against odour from the sewer.

Even if connected to a trapped Gully downstream there is still a risk of backflow and/or detritus collecting in the run which wouldn't cause too pleasurable a smell, especially in hot weather!